Page 62 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani
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strength were measured in two directions. First in the direction that the scaffold was built (building direction, x) and second in the direction perpendicular to the building direction (side direction, y; Fig. 1e). Compressive and tensile strength of the gradient scaffolds were measured in the upper half and in the lower half of the scaffold separately. Therefore, the scaffold was placed on the universal testing machine platform horizontally, either the side of the building direction or the side direction facing up, while the load cell was in contact with 1 cm × 1cm area of the scaffold (half of the scaffold) and therefore, the load was applied only to half of the scaffold (Fig. 1e). The cross sectional area was measured using a caliper prior to mechanical testing. A 1 kN load cell was used at a cross head speed of 1 mm/min for the compression test and 0.3 mm/min for the tensile test. Values of load F (N) and time (s) were recorded. Stress values (MPa) were determined by dividing the load (N) by the cross sectional area of each specimen (mm2). Strain values were determined by dividing displacement values (mm) by the initial height of the specimen. Stress- strain curves were plotted and compressive strength was determined by 1% offset of the first linear section. Compressive and tensile modulus were determined as the slope of the first linear region of the stress-strain curves.
Computational fluid dynamics model
A finite element model was used to assess the influence of interstitial fluid flow on fluid shear stress and fluid pressure inside the homogeneous and gradient-structured scaffolds. The modeling was performed in a 3D-scaffold measuring 1×1×2 cm (length×width×height; total volume, 2 cm3; Fig. 2a). Structured volume mesh with a total number of 1988304 elements (number of tetrahedral elements: 336802; prism elements: 232022; triangle elements: 139276;
-4 3 edge elements: 32218), an element volume ratio of 4.106×10 , and mesh volume of 1130 mm
was used to accurately calculate the FE model (Fig. 2b). The magnitude of the inlet flow rate was 2 𝜇𝜇𝜇𝜇m/s, which was measured as fluid flow in the tissue interstitium [27, 28].
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